Seismic collapse safety and response modification factor of concrete frame buildings reinforced with superelastic shape memory alloy (SMA) rebar

Seismic performance of concrete frame buildings reinforced with superelastic Shape Memory Alloy (SMA) rebar is evaluated in terms of Collapse Margin Ratio (CMR). CMR is the ratio of the ground motion intensity at the median collapse to the Maximum Considered Earthquake (MCE) ground motion intensity at the fundamental period of the building frame. The results are compared with the performance of concrete frames reinforced with regular steel rebar only. Collapse safety assessment is performed using both nonlinear static pushover and nonlinear Incremental Dynamic Analysis (IDA) with 20 ground motion records. For analysis, three different stories (3, 6 and 8) of Reinforced Concrete (RC) buildings, each with four different types of reinforcement detailing, are considered: (i) steel reinforcement (Steel) only and (ii) SMA rebar used in the plastic hinge region of ground floor columns and steel rebar in other regions (SMA-CM) (iii) SMA rebar used in the plastic hinge region of all the beams and steel rebar in other regions (SMA-BM) (iv) SMA rebar used in the plastic hinge region of both beams and ground floor columns (SMA-BM-CM). Results indicate an increase in collapse capacity for 3 and 8 story concrete frame structures while using SMA as reinforcement. The seismic response modification factor for concrete frame reinforced with shape memory alloy has also been evaluated based on an acceptable collapse margin ratio according to the guidelines provided in FEMA P695.